Compass jellyfish in Boka Bay, Montenegro

Jellyfish...so graceful and elegant, yet at the same
time found in so many different colors and shapes. Their movements remind you
of an underwater dance. They are a real pearl of the sea, ocean and assorted
lakes. But if the food chain is being disrupted, they can became a problem for
certain environments.

Jellyfish
are regularly found in the Bay of Kotor. In
2014, Chrysaora hysoscella, also known as the Compass Jellyfish, were last seen
in large numbers around the area. Composed of 96% water, the adult Compass Jellyfish
can grow up to 40cm in diameter across their bell-shaped
body. The “frilly” circumference of the Compass Jellyfish helps it to find its way around
and sense its orientation in the water. This species of jellyfish has 24 tentacles
organized in groups of three around the edge
of the bell which can reach up to 2 meters in length. The four mouth arms hanging
down from the centre are armed with nematocycts, the stinging mechanisms designed
to subdue their prey. Their sting, as much as it can be very painful to humans, is not very dangerous.

Compass
Jellyfish appear in greater numbers in the spring as this is their budding season. Following a brief period
attached to the seabed, their polyps hatch and develop into large aggregations
of jellyfish which are born male at first and turn into females later in life. Their
life expectancy is just one year, and often
up to 95% of their population dies off as they are unable to swim against
strong currents and they get washed up onshore. As large quantities of
jellyfish and other gelatinous sea creatures are
found in all of the world’s oceans, greater attention is being given to this species. Large aggregations
of the species can burst fishing nets, block inflows/outflows
on marine vessels and cause an adverse influence on both fishing and
aquaculture.

The
natural predators of this species of jellyfish include the leatherback turtle (Dermochelys coriacea) and sunfish (Mola Mola), neither are present in
Montenegrin waters in sufficient quantities to threaten the jellyfish
population or to regulate their numbers. They are an important part of the
marine food chain feeding on fish eggs and larvae, which controls
the growth and development of fish stocks in affected areas.

Katie on Aug 02nd 2017This is an interesting article as we have lived on a boat in Kotor bay for many years and were surprised to see so many of these jellyfish in spring this year, 2017. They disappeared after a few weeks but today (2 August) we have seen around 200 of them, of different sizes but mainly young, in Kotor Bay. Do you have any idea of how long they might hang around here? It is good to see wildlife here (lots of turtle sightings this summer in the bay), but not great for swimming! I assume they give a nasty sting? Thanks for the article - now I know what type of jellyfish they are!

James Griffin on May 13th 2017Stunning photography , and a very interesting read.